In general, the invention relates to controlling an ion flow which should be controlled in a clocked manner, for example in an analysis appliance such as an ion-mobility spectrometer. A so-called ion gate can be used to influence the ion flow. In this context, the invention relates, in general, to the field of ion-mobility spectrometry and the associated appliances, i.e. of ion-mobility spectrometers and gas analysis devices formed therewith.
Such a gas analysis device with an ion-mobility spectrometer is described in WO 2015/091146 A1.
Ion-mobility spectrometers are appliances for the fast and highly sensitive analysis of trace gases, said ion-mobility spectrometers separating and identifying substances on the basis of the movement of their ions through a neutral gas under the influence of an electric field. Here, the so-called time-of-flight ion-mobility spectrometer represents a conventional embodiment; it measures the time that ions need to pass over a defined path. It consists of four main components—an ion source, which produces ions, an ion gate, which allows an ion packet to pass at periodic intervals, a drift path, along which the time-of-flight is measured, and a detector which records the incident ion flow. Since instances of ion packet broadening at the start time are directly reflected in scattering of the observed time-of-flight or in instances of ion packet broadening at the detector, and thus reduce the analytic capability, a fast ion gate represents an important component of every time-of-flight ion-mobility spectrometer. Consequently, an optimized ion gate would be of great interest to each of these devices. Inter alia, the ion gate is also referred to as gate or shutter; the transfer of ions from the ion source into the drift path is also referred to as injection.
The ion gate described in WO 2015/091146 A1, having the arrangement made of three successive electrodes, already has many advantages; in particular, the three-electrode structure allows a distortion of the field, produced by the field generating device, for transporting the ions to be minimized. However, the procedure described therein for operating the ion gate leads to discrimination against slower ion species; i.e., such slow ions are excluded from the analysis since they are often unable to pass the ion gate within the required time.